An acrylic plate is widely used for a light guide of a planar light-emitting device of edge light type, such as a liquid crystal television, but, from the viewpoint of stiffness, heat resistance and water resistance, its replacement by a glass plate has been studied.
When a glass plate is applied as such a light guide, however, it has become apparent that as the optical path length becomes longer by a larger screen, light absorption inside the glass plate in the visible light region (wavelength of from 380 to 780 nm) tends to be not negligible, thus leading to a problem such as reduction of brightness or in-plane unevenness of brightness/color.
Therefore, as glass for the light guide, a glass article is required to have the influence of variation in light absorption inside of the glass plate further suppressed.